Anchor Loads - Which size of swivel?

Tim Good

Tim Good

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So after reading the recent anchor dragging post and heading Vyv's advice on his page I am replacing my damaged Kong Swivel. Like him mine got snagged at an angle when using a bow shackle. I like the idea of the shackle rather than just attaching it directly to the chain so I will replace my Kong and add 3 links of chain between it and the anchor.

However, I how much force am I expected to have on a worse case scenario anchoring in 60kts of wind. I currently have 10mm chain the AC10-S size which is for 8-12mm chain and a SWL of 2000kg breaking at 5000kg. These cost approx £63 from Jimmy Green.

The reason I ask, rather than just going up a size as default, is that the next size (KGAC12-S) is £211 :eek:

Therefore I deemed it worth asking the question as I'm unsure what sort of loads are really put on anchors in the thick of it.

NOTE: I have a 100m of 10mm chain with a decent anchor on a 18t boat.
 
northcave said:
So after reading the recent anchor dragging post and heading Vyv's advice on his page I am replacing my damaged Kong Swivel. Like him mine got snagged at an angle when using a bow shackle. I like the idea of the shackle rather than just attaching it directly to the chain so I will replace my Kong and add 3 links of chain between it and the anchor.

However, I how much force am I expected to have on a worse case scenario anchoring in 60kts of wind. I currently have 10mm chain the AC10-S size which is for 8-12mm chain and a SWL of 2000kg breaking at 5000kg. These cost approx £63 from Jimmy Green.

The reason I ask, rather than just going up a size as default, is that the next size (KGAC12-S) is £211 :eek:

Therefore I deemed it worth asking the question as I'm unsure what sort of loads are really put on anchors in the thick of it.

NOTE: I have a 100m of 10mm chain with a decent anchor on a 18t boat.
Click to expand...

The swivel needs to have a breaking strength larger, higher, than your chain. In fact everything needs to have a breaking strength larger than your chain, so your shackles also.

Your swivel should be loaded 'in line' but the shackle can be side loaded and most shackles on side loading would have a breaking strength halved from in line loading (so a shackle with a breaking strength of 6t is now only 3t - worst case scenario. I'd be using a rated shackle.

But if you have 10mm chain (G3 or G4??) and it is the weak link, everything else being stronger - that defines what load you need to cater for.

The greatest loads can occur when you retrieve - so forget about catenary, snubbers etc - its that snatch load on the immovable anchor when a wave hits your bow at the point when your anchor chain is vertical.

Jonathan
 
I only tested swivels for 8 mm chain, and 10 mm shackles that will normally fit 8 mm links. The results are all on the website but to summarise, well made ones from known manufacturers were all stronger than the chain. Kong and Osculati give SWL values that are for transverse loading, i.e. the swivel joint in bending. Adding in links of chain prevents this from happening, so the SWL will be considerably higher than the rated figure. In fact the given SWL of 850 kg is quite similar to the figure for 8 mm chain, which gives more reassurance.

So far as whether a swivel is necessary, my advice is if you don't find the need, don't buy one. My windlass manufacturer recommends using one and I have found during a season without one that having a swivel gives significant advantages.
 
Thanks.

I have ordered the SWL 2000kg version for 8-12mm chain and Jimmy Green kindly threw in 3 links of 12mm chain free of charge which was nice.

Just for reference here is a photo of my swivel as it is now:

11220460_10153557683113162_7976408263904622096_n.jpg


11988192_10153557684738162_1734268615438831390_n.jpg
 
northcave said:
I have ordered the SWL 2000kg version for 8-12mm chain and Jimmy Green kindly threw in 3 links of 12mm chain free of charge which was nice.
Click to expand...
Isn't the 12mm chain supposed to go between the anchor shank and the swivel ?

Boo2
 
northcave said:
Thanks.

I have ordered the SWL 2000kg version for 8-12mm chain and Jimmy Green kindly threw in 3 links of 12mm chain free of charge which was nice.

Just for reference here is a photo of my swivel as it is now:
Click to expand...

Are you sure this swivel is from KONG. Given the construction shown in the picture I highly doubt it. There should be a marker on the side with the logo of Kong (http://www.kong.it/en/2-products/items/f41-sailing-accessories/p622-swivel-anchor-connector)

For my anchor I had a steel welder create an oval ring on the shank of the anchor. I use that as connection point for the swivel. That way the jaws of the swivel cannot be caught by the shank.
 
aluijten said:
Are you sure this swivel is from KONG. Given the construction shown in the picture I highly doubt it. There should be a marker on the side with the logo of Kong (http://www.kong.it/en/2-products/items/f41-sailing-accessories/p622-swivel-anchor-connector)

For my anchor I had a steel welder create an oval ring on the shank of the anchor. I use that as connection point for the swivel. That way the jaws of the swivel cannot be caught by the shank.
Click to expand...

That's the OPs old Force 4 type swivel which he's replacing. On mine the Allen bolts at each end had bowed slightly. Now replaced with a Kong as per the OPs intention.

Richard
 
We were anchored in a Greek island bay and the wind picked up at night and reversed, in the morning there were three boats on the rocks all had swivels. What I found was if the chain was twisted in clear water you could see the anchor turning and taking the twists out, it was a CQR.
 
Maybe not that relevant, but i've found that as with most things these days.... QUALITY rather than quantity seems to be the key. Junking my crappy old 10mm chain, non branded, yet outrageously heavy swivel link, and again non branded anchore, has enabled me to step down to 8mm quality chain and appropriate sized 'Kong' swivel, and a considerably lighter anchor.

A MASSIVE weight saving up the pointy end, and much easier to work with.
 
N
northcave said:
Thanks.

I have ordered the SWL 2000kg version for 8-12mm chain and Jimmy Green kindly threw in 3 links of 12mm chain free of charge which was nice.

Just for reference here is a photo of my swivel as it is now:

11220460_10153557683113162_7976408263904622096_n.jpg


11988192_10153557684738162_1734268615438831390_n.jpg
Click to expand...

Nice photos that illustrate perfectly the problem with only using a shackle, not the extra links of chain. See how the jaws of the swivel have bent when they have been jammed against the anchor.

This swivel looks to be the same one I had that failed in San Antonio. The wind strength was negligible, less than 10 knots. Failure probably due to stress corrosion cracking, certainly intergranular in nature. Basically poor manufacturing technique.
 
NormanS said:
Swivels, a sure and shiny solution for a nonexistent problem. :rolleyes:
Remind me what they actually achieve?
Click to expand...

I too am keen to learn about swivels. I have one now with a CQR, but not really sure what it achieves. I do get chain twisting on retrieval, but usually swing the anchor just as it breaks surface to cure this.
When my new anchor arrives and I fit it, I'm still not sure if I need a swivel.
 
I'd dump that stainless shackle, which is one of the weak links. Get yourself a decent rated, galvanised shackle. Ideally you want a Grade B shackle. Also make sure any clevis pin is moused in the future.

These anchors with a round hole in the shank, will not take the eye of a bow shackle, should always have an over large 'D' shackle, so the clevis pin should be as large as you can fit in the hole - within reason. You can then fit a bow shackle the 'right way' round (or add extra links).

Galvanised Grade B shackles, available from Crosby, Peerless and Campbell (sadly all American). You can buy Crosby in the UK (Technilift? Tecnilift?), not sure about Peerless (they have a German outlet, stocking their metric chain,- email them in America) nor Campbell. Most, all?, European rated shackles are Grade A and half the strength of a Grade B shackle. They cost peanuts. See Practical Sailor August and September 2015.

Jonathan
 
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Neeves said:
You can buy Crosby in the UK (Technilift? Tecnilift?), not sure about Peerless (they have a German outlet, stocking their metric chain,- email them in America) nor Campbell.
Click to expand...

Thanks. Yes I'm buy some Crosby ones at the moment for my series drogue. They're the only ones to do the SWL I need within a specific size which they get in their new alloy versions. Anyway I'll get one for the anchor at the same time.
 
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